U.S. patent number 4,963,745 [Application Number 07/402,959] was granted by the patent office on 1990-10-16 for octane measuring process and device.
This patent grant is currently assigned to Ashland Oil, Inc.. Invention is credited to Steven M. Maggard.
United States Patent |
4,963,745 |
Maggard |
October 16, 1990 |
Octane measuring process and device
Abstract
The near infrared absorbance of the methyne band measures octane
(pump, RON, and MON) with excellent correlation and can be used for
gasoline blending. The absorbance may be measured as the first,
second, third, fourth or higher derivative or by other signal
processing techniques. The signal can be used to control a
multi-component gasoline blending system to produce a preset
desired octane. Such continuous or frequent measurement of octane
(research octane number, RON; motor octane number, MON; and pump
octane number (research plus motor times 0.5)) permits constant or
frequent optimization of gasoline blending to produce a target
octane which is sufficient to meet motorists' needs, yet uses
minimum amounts of the more expensive high octane blending
stocks.
Inventors: |
Maggard; Steven M. (Huntington,
WV) |
Assignee: |
Ashland Oil, Inc. (Ashland,
KY)
|
Family
ID: |
23593973 |
Appl.
No.: |
07/402,959 |
Filed: |
September 1, 1989 |
Current U.S.
Class: |
250/343;
250/339.12 |
Current CPC
Class: |
G01N
21/359 (20130101); G01N 21/3577 (20130101); G01N
33/2829 (20130101) |
Current International
Class: |
G01N
21/31 (20060101); G01N 21/35 (20060101); G01N
33/28 (20060101); G01N 33/26 (20060101); G01N
021/59 () |
Field of
Search: |
;250/343,341,339 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
4800279 |
January 1989 |
Hieftje et al. |
|
Foreign Patent Documents
Other References
"Near-Infrared Reflectance Analysis by Gauss-Jordan Linear
Algebra", D. E. Honigs, J. M. Freelin, G. M. Hieftje, T. B.
Hirschfeld, Applied Spectroscopy, vol. 37, No. 6, 1983, pp.
491-497. .
"Prediction of Gasoline Octane Numbers from Near Infrared Spectral
Features in the Range 660-1215 nm", by J. J. Kelly et al.,
Analytical Chemistry, vol. 61, No. 4, Feb. 15, 1989, pp.
313-320..
|
Primary Examiner: Fields; Carolyn E.
Attorney, Agent or Firm: Willson, Jr.; Richard C.
Claims
What is claimed is:
1. In a process for the determining of octane number or other
measure of knock avoidance of a fuel by near infrared range
spectroscopy, the improvement comprising determining said octane
number or other measure of knock avoidance by:
a. measuring absorbance in the t-butylmethyne band;
b. periodically or continuously outputting a periodic or continuous
signal indicative of the intensity of said absorbance in said band
or one mathematical function or a combination of mathematical
functions thereof; and
c. mathematically converting said signal to an output signal
indicative of said octane number or other measure of knock
avoidance of said fuel.
2. A process according to claim 1 wherein said fuel flows
substantially intermittently or continuously past the point where
said measurement is being made.
3. A process according to claim 1 wherein a derivative of said
absorption of said t-butyl/methyne band is measured.
4. A process according to claim 3 wherein a derivative of said
absorption of said t-butyl/methyne band is the first
derivative.
5. A process according to claim 3 wherein a derivative of said
absorption of said t-butyl/methyne band is the second
derivative.
6. A process according to claim 3 wherein a derivative of said
absorption of said t-butyl/methyne band is the third
derivative.
7. A process according to claim 3 wherein a derivative of said
absorption of said t-butyl/methyne band is the fourth or higher
derivative.
8. A process according to claim 1 wherein the fuel is gasoline and
the octane number measured is pump octane number.
9. A process according to claim 1 wherein the fuel is gasoline and
the octane number measured is motor octane number.
10. A process according to claim 1 wherein the fuel is gasoline and
the octane number measured is research octane number.
11. A process according to claim 1 wherein said signal controls a
fuel blending system feeding blending components having different
octane numbers into a common zone, whereby a fuel product having a
desired octane number is produced.
12. A process according to claim 11 wherein each component is
analyzed by a near infrared analyzer to produce a signal and all
such signals are inputted to a computer controlling the blending
process.
13. A processing according to claim 1 wherein said fuel is a
gasoline.
14. A process according to claim 2 wherein said fuel is a
gasoline.
15. A process according to claim 3 wherein said fuel is a
gasoline.
16. A process according to claim 5 wherein said fuel is a
gasoline.
17. A process according to claim 1 wherein absorbance in one or
more additional bands is measured and a signal indicative of its
respective absorbance is combined with said signal indicative of
absorbance in said t-butyl/methyne band.
18. A process according to claim 17 wherein said one or more
additional bands comprise at least one band selected from the group
of methyl, methylene, aromatic and substituted aromatic bands.
Description
BACKGROUND OF INVENTION
Because the well known knock engine method of measuring fuel octane
or other measure of knock avoidance is not continuous, requires an
internal combustion engine under load, and involves spark hazard
and substantial maintenance; a continuous method for measurement of
octane number, etc. has long been sought.
Kelly, Barlow, Jinguji and Callis of the University of Washington,
Seattle, (Analytical Chem. 61, 313-320,) found gasoline octane
numbers could be predicted from near infrared absorbance in the
range 660-1215 nanometers (nm). They found best correlation between
absorbance and octane number to occur at 896, 932 and 1164 nm for
research octane number, 930, 940 and 1012 nm for motor octane
number, and 896, 932 and 1032 nm for pump octane number.
A search in Lexpat (U.S. patents from 1975 forward) under infrared,
octane, and (gasoline or fuel) within 25 words of each other showed
only four patents: U.S. Pat. Nos. 4,277,326; 4,264,336; 3,496,053;
and 903,020, none of which relate to new techniques for the
measurement of octane.
The present invention, by measurement of absorbance in a range
close to but above the Kelly et al. wavelengths, shows dramatically
improved correlation as compared to measurements made in the
wavelengths described by Kelly et al.
SUMMARY OF THE INVENTION
According to the present invention, any of the three octane numbers
(or all of them) can be measured (predicted) by measuring the near
infrared absorbance in the methyne range (1200 to 1236 nm). This
range correlates sufficiently closely to permit in-line (or
at-line, measuring a smaller sidestream) measurement to control
blending systems to produce gasolines of target octane with close
accuracy.
Preferably, the absorbance in the methyne range is converted into
an electrical signal which is preferably combined with signals
indicative of absorbance in other ranges, most preferably about
1196 nm and 1236 nm.
Octane
As mentioned above, the present invention is useful for the
measurement and control of systems producing octanes according to
the well known knock engine procedures for RON, MON, and pump
[(R+M)/2] octane. Pump octanes measured are preferably in the range
of from about 75 to 120, and most preferably from about 84 to
95.
Signal Processing
As those skilled in the art will be aware, the absorbance signal
from the measurement of the methyne and other bands will preferably
be mathematically processed to provide derived signals which are
more directly indicative of the octane being measured. Preferred
techniques for mathematical processing are the first, second,
third, and fourth or higher derivative. The technique of dividing
the absorbance at one wavelength by the absorbance at all other
wavelengths in order to cancel out background or noise and
normalize the signal; spectral subtraction in which the spectrum of
one sample is subtracted from the spectrum of another sample in
order to differentiate differences in absorbance, and various
combinations of these mathematical techniques. Also valuable are
well known curve fitting techniques, e.g. Savitsky-Golay curve fit,
Kubelka-Munk curve fit transformation, and n-point smoothing
(signal averaging).
Theory
While the invention is claimed independent of any underlying
theory, the invention appears to relate to the free radical
propagation and stability of the fuel being analyzed. It is
hypothesized that ease and smoothness of combustion are probably
related to the free radical stability of the species generated
during the process of combustion, e.g. secondary and tertiary free
radicals. The methyne band, along with the tertiary butyl band
(1200-1236 nm), is indicative of methyne groups and t-butyl groups,
respectively. The presence of methyne groups and t-butyl groups
affords a source of stable free radicals which smooth the
combustion process in contrast to the less stable compounds which
give rise to sudden changes in combustion which result in knocking
of the internal combustion engine in which the fuel is being
consumed. Octane is the measure of the ability of the engine to run
under adverse circumstances and heavy loads without substantial
knocking. 1985 Annual Book of ASTM Standards, Volume 05.04 Test
Methods for Rating Motor, Diesel and Aviation Fuels, American
Society for Testing and Materials; Philadelphia, Pa., 1985.
Analytical Equipment
Near Infrared spectrometers and modified IR spectrometers of
convention design may be used with the invention. Preferred modes
of operation are transmission, reflectance, and transreflectance.
Suitable spectrometers are the NIRSystems Model 6500; LT Industries
Model 1200; and the Guided Wave Model 300 Series. The spectrometer
can be operated on a batch basis (receiving signals, e.g. by a
sample feeding arrangement), or, more preferably, on a continuous
basis in which the fluid to be measured flows through a cell or a
probe immersed in the flowing fluid transmits optically through a
fiber-optic cable to the spectrophometer. The techniques for
sampling, measuring, and signal processing can be conventional and
are well known to those skilled in the art.
Blending Systems
Blending systems for use with the present invention can be of
conventional design, usually involving the use of proportioning
pumps or automatic control valves which control the addition rate
for each of a series of components fed from different tanks or
other sources. A computer receiving the output signal from the
spectrophotometer can readily process the information to not only
provide the target octane number in the finished blended gasoline,
but also to provide the target octane at minimum cost, given the
relative costs and octane enhancement values of the components
being fed to the blending system.
Utility of the Invention
As described above, the invention will be useful in the blending of
gasoline, less preferably diesel fuels (cetane number) and jet
fuels, e.g. JP4, both in refineries and in large fuel storage
terminals. Blending can be into storage tanks, tank trucks, rail
cars, barges, or other transportation vehicles. An allowance for
octane depletion during transportation based on expected weather
conditions can also be included in determining the target octane
for blending. Additionally, the invention will be useful for
monitoring gasoline quality at retail outlets to assure quality
control specifications.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plot of the preferred second derivative of absorbance
versus wavelength (d.sup.2 A/d, nanometers) and shows the near
infrared band assignments for the methyl, methyne, t-butyl and
methylene functional groups.
FIG. 2 is a plot of multiple correlation versus wavelength, showing
the excellent correlation obtained with the methyne and t-butyl
groups. Note the change in the correlation at 1228 nm from strongly
positive to negative as the scan proceeds from the t-butyl and
methyne groups to the methylene.
FIG. 3 shows the second derivative of the methyne and methyl
absorption bands in the near infrared versus the wavelength for
some selected compounds. Note the cumene and 2,3,4-trimethyl
pentane do not contain methylene groups. This demonstrates that the
methyne band position in the second derivative spectrum extends
from 1202 to 1236 nm.
FIG. 4 similarly shows that t-butyl group (e.g. of the methyl
tertiary butyl ether, MTBE, a popular gasoline octane enhancer
additive) also falls within the methyne absorption range. The
t-butyl band is centered between 1200-1232 nm.
FIG. 5 is the Savistsky-Golay curve fit of the spectrum of
2,3,4-trimethyl pentane and 2-methyl pentane showing the methyne
absorbance in the transmission spectrum.
FIG. 6 is a schematic diagram of a gasoline blending system
utilizing the octane measurement techniques of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
EXAMPLE I
A series of samples of about 141 blended gasolines are analyzed for
pump octane number (RON plus MON divided by 2) by measuring the
near IR absorbance at 1220, 1196, and 1236 nm. The second
derivative is taken of each absorbance measured and is used to
perform a multiple regression. The multiple regression analysis of
the data essentially fits the curve; ##EQU1## all as shown in Table
A.
TABLE A ______________________________________ Regression Results
File name: OCT2ND Instrument: 6500 Standard error = .345 No. of
spectra: 141 Multiple R = .9927 Constituent: 3, PUMP Math: 2nd
derivative Segment: 20 Gap: 0 Constants Wavelength Simple R K(0) =
85.506 K(1) = 70.323 1220 .988 K(2) = 16.465 1196 .385 K(3) =
28.615 1236 -.951 ______________________________________
The multiple coefficent of correlation between the octane, y, and
the second derivatives of the absorbances is 0.9927, a very close
correlation. This is equivalent to a standard error of about plus
or minus 0.345 octane numbers which is better than can generally be
accomplished by a knock engine with a skilled operator (the average
of ASTM methods 2699-84 and 2700-84).
EXAMPLE II
FIG. 1 shows a plot of the second derivative of the near infrared
absorption spectra of approximately 142 gasoline samples, analyzed
by the techniques of Example I. Also plotted on FIG. 1 are the
second derivative ranges of the methyl (1174 to 1212 nm),
t-butyl/methyne (1212 to 1228 nm), and the methylene (1228 to about
1268 nm). These absorptions are in the second overtone region of
the near infrared spectrum. That is, the original absorbance band
for the methyl, methyne, t-butyl and methylene groups is at about
3367 nm, so these near infrared ranges being measured are overtones
similar to harmonics of the original bands. Working in the second
overtone has advantages over the third overtone which was used by
Kelly et al. For example, at a total path length of 20 mm, the
absorbance measurements in the second overtone region are in the
region where the Beer-Lambert Law is obeyed, whereas in the third
overtone region they are not. (Note, Kelly et al used a 20 mm path
length, 10 mm cell in reflectance mode.)
EXAMPLE III
Table B shows techniques similar to those used in Example I, but
utilizing only the 1220 nm wavelength (methyne range). The multiple
correlation is 0.9836 and is the highest correlation of any single
wavelength in the near infrared range (800-2500 nm) with motor
octane number.
TABLE B ______________________________________ Regression Results
File name: OCT2ND Instrument: 6500 Standard error = .524 No. of
spectra: 141 Multiple R = .9836 Constituent: 2, MON Math: 2nd
derivative Segment: 20 Gap: 0 Constants Wavelength Simple R K(0) =
75.158 K(1) = 59.949 1220 .984
______________________________________
EXAMPLE IV
When techniques similar to those described in Example III on
research octane number, the correlation between RON and the second
derivative of absorbance at the 1220 nm wavelength is 0.9649
indicating a standard error of plus or minus 0.752 octane numbers,
the best correlation and lowest standard error available with any
single wavelength in the near infrared range. (see Table C)
TABLE C ______________________________________ Regression Results
File name: OCT2ND Instrument: 6500 Standard error = .752 No of
spectra: 141 Multiple R = .9649 Constituent: 1, RON Math: 2nd
derivative Segment: 20 Gap: 0 Constants Wavelength Simple R K(0) =
84.408 K(1) = 57.980 1220 .965
______________________________________
EXAMPLE V
When techniques similar to those described in Example III are used
to determine pump octane number, the correlation between RON and
the second derivative of absorbance at the 1220 nm wavelength is
0.9878 indicating a standard error of plus or minus 0.442 pump
octane numbers, the best correlation and lowest standard error
available with any single wavelength in the near infrared range.
(see Table D)
TABLE D ______________________________________ Regression Results
File name: OCT2ND Instrument: 6500 Standard error = .442 No. of
spectra: 141 Multiple R = .9878 Constituent: 3, PUMP Math: 2nd
derivative Segment: 20 Gap: 0 Constants Wavelength Simple R K(0) =
79.782 K(1) = 58.962 1220 .988
______________________________________
EXAMPLE VI
FIG. 5 shows the results of subtracting the absorbance versus
wavelength spectrum of n-hexane from 2,3,4-trimethyl pentane using
a Savitski-Golay curve fit. From this figure, one can see that
without mathematical treatment the methyl band extends from about
1160-1195 nm, the methylene band from about 1195-1200 nm, and the
methyne band is from about 1230-1250 nm.
EXAMPLE VII
Comparative
When techniques similar to those described in Example III are used
to determine pump octane number, but using the regression model and
wavelengths of Kelly et al., the correlation between pump octane
number and the second derivative of absorbance at the 896, 932 and
wavelength is 0.9841 indicating a standard error of plus or minus
0.497 pump octane numbers (but using 90 samples) as set forth in
Table E. Thus, the present invention with only a single wavelength
measured provides accuracy better than the multiple correlation
suggested by Kelly et al.
TABLE E ______________________________________ (Kelly Wavelengths)
Regression Results File name: GASMINUS Instrument: 6500 Standard
error = .497 No. of spectra: 90 Multiple R = .9841 Constituent: 1,
PUMP Math: N-Point smooth Segment: 2 Gap: 0 Constants Wavelength
Simple R K(0) = 100.105 K(1) = 278.370 896 .236 K(2) = -768.856 932
-.943 K(3) = 305.203 1032 -.453 (Invention) Regression Results File
name: GAS2ND Instrument: 6500 Standard error = .414 No. of spectra:
90 Multiple R = .9887 Constituent: 3, PUMP Math: 2nd Derivative
Segment: 20 Gap: 0 Constants Wavelength Simple R K(0) = 79.756 K(1)
= 59.253 l220 .989 ______________________________________
EXAMPLE VIII
FIG. 6 is a schematic diagram of a typical gasoline blending system
such as might be used to employ the present invention at a refinery
or large terminal. Tanks 10 through 15 contain gasoline blending
stocks, e.g. reformates, isomerates, alkylates, etc. Each of these
components has its own octane value as well as a price. For
example, reformate and alkylate are both high in octane number, but
are relatively expensive blending stocks. Each of the tanks has an
automatic control valve 16 through 21 which controls the flow of
the particular blending stock from the tank into a common header 22
and thence into mixing tank 23 from which pump 24 moves the blended
gasoline through "at-line" analyzer 25 which analyzes the near IR
absorbance of a side-stream 30 at 1220 nm, 1196 nm, and 1236 nm,
and transmits the resulting absorbance measurements to a
mathematical conversion device 26 which converts the signal into
the second derivative and feeds the resulting signal to computer
27. Optional display device 28 can display both the target octane
and the measured octane number at all times. The output from
computer 27 is fed to each individual control valve (or
proportioning pump) 16 through 21, and controls the relative flow
of each of the gasoline blending components 10 through 15 into the
blending tank 23. Various adjustments can be made for hold-up in
the tank, etc. (Alternately, the functions of the mathematical
conversion device 26 can also be performed by computer 27.)
The resulting gasoline is within plus or minus approximately 0.3
octane numbers at all times.
In another variation, each of the lines from the gasoline blending
stock tanks 10-15 is fitted with a near IR analyzer (like 25) which
inputs a signal to the computer 27 which is now programmed to
control and optimize the blending process based on all these
inputs.
In another variation, an operator reads the computer output of
octane number and manually or mechanically controls and optimizes
the blending process.
Modifications
Specific compositions, methods, devices or embodiments discussed
are intended to be only illustrative of the invention disclosed by
this specification. Variation on these compositions, methods, or
embodiments will be readily apparent to a person of skill in the
art based upon the teachings of this specification and are
therefore intended to be included as part of the inventions
disclosed herein. For example, individual variations of NIR
spectrometers could cause the optimal wavelengths to be shifted
slightly since the precise location of any wavelength is inexact.
Also, since differing crude oils produce gasolines which are of
differing molecular structures, it is highly likely that a
different wavelength might show higher correlations for the
selection of the initial wavelength. It should be noted that the
methyne group could still be valuable in conjunction with the first
wavelength.
Reference made in the other specification is intended to result in
such patents or literature being expressly incorporated herein by
reference including any patents or other literature references
cited within such patents.
* * * * *